"To my mother, Ayn Rand, and God" can be interpreted as a list of 3 people (1, my mother; 2, Ayn Rand; 3, God) or a list of 2 people (1, my mother, who is Ayn Rand; 2, God). Removing the Oxford comma makes this dedication much clearer: "To my mother, Ayn Rand and God".

However, if the attribution were to the author's parents instead of the author's mother, the sentence becomes "To my parents, Ayn Rand and God" which can be interpreted as a list of 4 people (1 and 2, my parents; 3, Ayn Rand; 4, God) or a list of 2 people (my parents, who are Ayn Rand and God). In this case, using the Oxford comma makes this dedication much clearer: "To my parents, Ayn Rand, and God".

All in all, it's just one big pile of fail and the style guides can't even agree on whether to support or oppose its usage.﻿

Comma is primarily used to communicate the structure of the sentence, i.e. what are the author of the sentence trying to communicate. As Kevin made it clear it is not as simple using one or the other exclusively. In the OP it doesn't matter at all, it's clear to all readers what the author had for breakfast. So use what makes sentence unambiguous, if both can be used pick one, but do yourself and your readers a favour and be consistent.﻿

Thurber was once asked by a correspondent: “Why did you have a comma in the sentence, ‘After dinner, the men went into the living room’?” And his answer was probably one of the loveliest things ever said about punctuation. “This particular comma,” Thurber explained, “was [_New Yorker_ editor] Ross’s way of giving the men time to push back their chairs and stand up.”

But see the Oxford comma discussion in the first few paragraphs ofhttp://www.timesonline.co.uk/tol/life_and_style/article838138.ece﻿

I'm with Susan, I was always taught in a list you didn't use the comma on the last thing in the list. That the "and" was all you needed. Then I got to college and a professor basically told us it really didn't matter either way but that it mostly was a matter of spacing and what gave a better flow to the sentence...curse you American English and your floppy grammar rules...﻿